Electric control system



March 26, 1940. E. E. MOYER El AL ELECTRIC CONTROL SYSTEM Filed Sept. 30, 1938 z w my m t m n eE Orrin W. Livin cgstofi,

TheiTAttoTfiey.

PM Mar. 26, 1940 2,195,119

UNITED STATES PATENT OFFICE ELECTRIC CONTROL SYSTEM Elmo E. Moyer, Scotia, and Orrin W. Iivingston, Schenectady, N. Y., assignors to General Electric Company, a corporation of New York Application September 30, 1938, Serial No. 232,598

15 Claims. (Cl. 171-419) Our invention relates to electric valve control a source of variable unidirectional voltage which systems and more particularly to electric valve varies in magnitude in accordance with the voltregulating systems for dynamo-electric machines. age of the armature winding of the synchronous Electric valve apparatus is particularly adaptcondenser, and also includes a serially-connected able to systems for controlling the operation of resistance and an electronic discharge device 5 dynamo-electric machines because of the rapidity which impress a variable biasing potential on of response of such apparatus. Electric valve control members of the electric valve means. The means are particularly suitable for use in voltage voltage drop appearing across the terminals of regulating systems for alternating current mathe resistance is limited by means of the current chines of the synchronous type, since the electric responsive circuit which responds to predetervalve means respond without appreciable. delay mined currents of predetermined power factor to variable voltage conditions, tending to intransmitted by the armature windings of the concrease the stability of synchronous systems. denser. The current controlling circuit is selec- Heretofore, electric valve apparatus has been aptively responsive to the power factor of the armaplied to excitation or control systems for vsynture current of the condenser and limits the cur- 15 chronous alternating current generators and synrent in the leading region of operation to a prechronous condensers. In accordance with the determined value. teachings of our invention described hereinafter For a better understanding of our invention there is provided an improved electric valve sysreference may be had to the following descripli tem for controlling synchronous alternating cur-- tion taken in connection with the accompanying rent machines, particularly synchronous condrawing, and its scope will be pointed out in the densers, whereby the system controls the conappended claims. The single figure of the accomdenser to distinguish between leading and lagging panying drawing diagrammatically illustrates an power factor of the current transmitted by ,the embodiment of our invention as applied to an exll armature windings of the condenser. citation system for energizing the field winding 26 It is an object of our invention to provide new of a synchronous condenser and in which the curand improved electric valve circuits. rent control circuit is responsive to the armature It is another object of our invention to provide current of the synchronous condenser. new and improved control or regulating systems In the single figure of the accompanying draw- 30 for dynamo-electric machines. ing'we have chosen to show our invention as ap- 30 It is a further object of our invention to proplied to an excitation system for an alternating vide new and improved voltage regulating syscurrent dynamo-electric machine, such as a syntems for alternating current machines 0! the chronous condenser I, having armature windings synchronous type. 2 and an excitation or field winding 3. The arma- It is a still further object of our invention to ture windings 2 may be connected to an alternat- 35 provide new and improved voltage regulating ing current circuit 4. Field winding 3 may be systems for synchronous condensers. variably energized by an exciter .5 having an In accordance with the illustrated embodiment armature winding 6, a shunt field winding I, and of our invention we provide a new and improved a series field winding 8. A suitable current cori- 40 voltage control or regulating system for syntrolling means, such as a variable resistance 9, 40 chronous condensers whereby the armature voltmay be connected in series relation with the age ofthe condenser is controlled and whereby series winding 8, if desired, and the positive terthe current in the leading region of operation is minal of the armature winding 6 may be conlimited in order to prevent an overload of the nected toone terminal of the shunt winding I condenser. The excitation or field winding 01 the through a switch ill and a current controlling 46 synchronous condenser is energized by an exresistance ii if it is desired to operate the exciter citer. and the field winding of the exciter is ener- 5 as a self-excited machine. gized from an alternating current circuit through The excitation of the synchronous condenser l electric valve means of the controlled type. The is controlled by the exciter 5, and the excitation s0 conductivities of the electric valve means are of the exciter 5 in turn is controlled by means of 60 controlled ccnjointly by means of a voltage dea circuit i2 comprising an alternating current termining or controlling circuit and by means of circuit it which may be connected to the altera circuit which is responsive to the power factor nating current circuit 4, if desired, and which of the armature current of the synchronous conalso comprises electric valve means It and I! denser. The voltage controlling circuit comprises and transformers It and I1. Suitable current 86 limiting devices such as fuses I! may be connected at various places in the circuit l2, as indicated, to protect the associated apparatus. Switches [9 and 2|! may be connected in the anode-cathode circuits of the electric valves l4 and I5 to disconnect these valves' when desired, and a switch 2| may be connected between circuit 2 and the exciter 5 if it is desired to operate the exciter 5 as a self-excited machine. Electric valve means H and I5 are preferably of the type employing an ionizable medium such as a gas or a vapor, and each comprises an anode 22, a cathode 23, a control member or grid 24, and a shield grid which may be connected to'the cathode 23. In order to dispense with the necessity of a phase shifting circuit where a displacement between anode-cathode and grid voltages is desired, we employ an arrangement as shown wherein the transformer H is connected to obtain a quadrature voltage from the transformer ii. The transformer i1 is employed substantially as an auto-transformer, and a surge arrester may be connected across a portion thereof to absorb transient voltages which may appear in circuit |3 to protect the electric valve apparatus. The surge arrester may comprise a serially-connected resistance 25 and a capacitance 21. In addition, if it is desired to suppress high frequency parasitic oscillations in the circuit |2. a filter circuit may be employed. We show a filter circuit comprising air core inductances 29 and 29 and capacitances 30 and 3|.

Alternating voltages of quadrature lagging phase displacement relative to the anode-cathode voltages of electric valves i4 and I5 are impressed on control grids 24 by means of a transformer 32 which is connected to be energized from transformer l6. Current limiting resistances 33 may be connected in series relation with the control grids 24. In order to balance the currents conducted by electric valves l4 and I5, we provide a voltage divider comprising serially-connected resistances 34, 35, and 38 which are connected across the secondary winding of transformer 32. Resistance 35 may be provided with an adjustable tap 31 to control the magnitude of the alternating components of voltage impressed on grids 24.

A voltage control or determining circuit 38 is employed to control the resultant voltage impressed on control grids 24 of electric valves l4 and I5 and hence controls the excitation and voltage of the synchronous condenser I. The voltage controlling circuit 38 is energized in accordance with the armature voltage of condenser I or in accordance with the voltage of circuit 4 through a transformer 39 and circuit 49. To produce a control voltage which varies in accordance with the voltage of circuit 4 or the armature voltage of condenser l, we employ a suitable rectifying circuit 4| which may be of the bi-phase type comprising a transformer 42 and a suitable unidirectional conducting device such as an electric valve 43. The output circuit of the rectifier 4| is connected to a suitable filter circuit 44 comprising inductances 45 and capacitances 46. As a means for amplifying the variations in magnitude of the variable undirectional voltage produced by rectifier 4|, we employ a suitable amplifier 47, such as that disclosed and claimed in copending patent application Serial No. 232,599 of E. E. Moyer, filed concurrently herewith, and assigned to the assignee of the present application. The amplifier 41 comprises a serially-connected impedance element, such as a resistance 48, and an electronic discharge device 49 having a common junction 48', and a constant voltage device or element such as a glow discharge valve 50 connected in' series relation across the output circuit of the rectifier 4| and the associated filter circuit 44. The electronic discharge device 49 is preferably of the high vacuum type having a control grid 5|, a screen grid 52 which is employed as a second control grid, and a suppressor grid 53. There is impressed on the control grid 5| a predetermined omponent of the variable unidirectional voltage supplied by rectifier 4| through a suitable voltage divider comprising serially-connected resistances 545|. A current limiting resistance 53 may be connected in series relation with the control grid 5|, if desired. In like manner, the screen grid 52 may be energized from a voltage divider which is connected to the output circuit of the rectifier 4| and which may comprise serially-connected resistances 59 and 50. A capacitance 5| may be connected between the lower terminal of the glow discharge valve 50 and the screen grid 52 to absorb extraneous transient voltages which may be present in the system. Output circuit 62 of circuit 41 may be connected to the common juncture of resistance 48 and electric valve 49, and to a point 63 of a resistance 64 which is connected between the positive terminal of the output circuit of rectifler 4| and the common juncture of the"electronic discharge device 49 and glow discharge valve 59. Point or tap 63 may be adjustable to permit adjustment of the resultant unidirectional biasing potential impressed on control grids 24 of electric valves l4 and I5.

We provide a, current controlling circuit which is responsive to the power factor of the armature current of the synchronous condenser and controls the voltage controlling circuit 33 to distinguish between leading and lagging current transmitted by the armature windings 2 of condenser The current controlling circuit 65 may include a current transformer 56 having a primary winding 61 which is connected in series relation with windings 2 and may include a transformer 68 having an adjustable primary winding 69, and an electronic discharge device 10. The electronic discharge device 13 may be of the high vacuum type or of the type employing an ionizable medium such as a gas or a vapor. We prefer to employ the former type. The electronic discharge device 19 serves as a controlled rectifier and also may be of the type comprising two electric discharge paths within a single envelope and may comprise anodes 1|, an electrically common cathode l2, and control grids 13. The anodecathode circuits of electronic discharge device II are energized from transformer 68, and a suitable voltage divider for effecting adjustment of the armature current control may be connected across the secondary winding of transformer 63. This voltage divider may comprise resistances I4, 15, and 16. Resistance 15 may be employed to effect the precise adjustment of the current controlling circuit 95, whereas the adjustable winding 69 of transformer 69 may be employed to effect the rough or coarse adjustment. Certain broad features of the circuit for controlling the system in response to the power factor are disclosed and claimed in copending patent application S. N. 211,453 of Richard Modlinger, filed June 2, 1938, and which is assigned to the assignee of the present application.

Control grids 13 of electronic discharge device 10 are energized in accordance with the voltage of armature windings 2 or in accordance with the voltage of circuit 4 through a transformer 'II which is connected to circuit; To obtain a neutral connection, a voltage divider comprising resistances 18 may be connected across the secondary winding of transformer 11.

To permit transient or short-time current overloads in the leading region of operation of the synchronous condenser .I, we provide a damping circuit I8 which is connected in the output circuit of the current controlling circuit 85. The damping circuit comprises inductances 88 and capacitances 8|. A relatively high impedance 82 may be connected across the output circuit of the current controlling circuit 85. As a means for bringing into operation the current limiting feature of the current controlling circuit 85, we employ a suitable unidirectional conducting device, such as an electric valve 83, which is connected between the output circuit of the current controlling circuit and resistance 48 01' circuit 42. So long as the voltage of circuit 85 remains below a predetermined value, electric valve 83 does not conduct current, and hence the circuit 41 operates substantially independently of circuit 85. However, if the leading current transmitted by the armature windings 2 of condenser I exceeds a predetermined value, the current controlling circuit 85 efi'ectively controls the circuit 38 to maintain a substantially constant condenser armature current.

The operation of the embodiment of our invention shown in the figure oi thedrawing will be explained by considering the system when the machine I is operating as a synchronous condenser. Exciter 5 transmits variable amounts of current to field winding 3 of condenser I in accordance with the voltage of circuit 4. The excitation of exciter 5 is controlled by circuit I2 which, in turn, is controlled by the voltage controlling circuit 38. Electric valves I4 and I5 conduct variable amounts of current to field winding 1 of exciter 5. It will be understood by those skilled in the art that the average current conducted by the electric valves I4 and I5 increases as the voltages impressed on the control grids 24 are advanced from a lagging position to one of phase coincidence with the anode voltages, and conversely, the anode circuit currents decrease as the grid voltages are displaced or retarded in phase. The resultant voltages impressed on the control grids 24 are comprised 01' two components, one being the alternating component displaced substantially electrical degrees relative to the anode-cathode voltages and obtained through transformers I8 and 32. The other component of voltage is the variable component of voltage derived from circuit 41.

Because many synchronous condensers are designed and constructed to deliver a predetermined amount of leading reactive volt-amperes to an associated circuit and by virtue of the rela tively high field excitation required to deliver this load, the maximum or limiting capacity of the condenser is usually established in that region of operation, Thus, it is important to limit the amount oi leading volt-amperes which the condenser may transmit. Furthermore, it is desirable in many instances to permit the condenser to transmit a large amount of lagging volt-amperes without imposing a limitation, since under such conditions'the field current is substantially reduced and the heating of the condenser is much less than when operating in the leading region. Circuit 85 cooperates with circuit 38 to limit the amount of leading reactive volt-amperes which the synchronous condenser I maydeliver. If it be assumed that the load transmitted by the condenser I is not excessive and is within the predetermined range of values, the voltage controlling circuit 38 varies the conductivity of electric valves I4 and I5 to maintain the armature voltage of condenser I substantially constant. Electronic discharge device 49 in circuit 38 transmits variable amounts of unidirectional current through resistance 48, and the voltage difference between points 48' and 83 is impressed on the control grids 24 of electric valves I4 and I5. Due to the fact that both control grids 5I and 52 .of electronic discharge device 43 vary in potential with the voltage changes of circuit 4, the amplification of circuit 41 is accentuated, efi'ecting precise control of the voltage of circuit 4.

So long as the armature current of condenser I does not exceed the predetermined range of values in the leading region of operation, circuit 38 controls the voltage of condenser I substantially independently of circuit 85. However, if the leading current exceeds a predetermined value, the output voltage of circuit 85 and hence the voltage appearing across resistance 82 attains a value sufilcient to cause electric valve 83 to conduct current. Upon being rendered conductive,

, excessive heating of the condenser.

If, on the other hand, the condenser I is transmitting lagging reactive volt-amperes to circuit 4, as, for example, when the voltage of circuit 4 tends to rise above a predetermined value. circuit 85 does not aiTect circuit 38 by virtue of the fact that the electronic discharge device 10 conducts a substantially smaller current than when the condenser I is transmitting leading reactive volt-amperes. This selective controlling operation of the circuit 85 is obtained by the manner in which the anode-cathode circuits and the grid circuits of electronic discharge device III are energized. Were it not for this selective controlling action of the circuit 85, the system would operate by locking in to cause the synchronous condenser I to supply a fixed amount of lagging reactive volt-amperes. Circuit 85, acting conjointly with the circuit 38, prevents the system from supplying a predetermined fixed number of lagging reactive volt-amperes and permits the desired control of the excitation of the synchronous condenser I within the lagging region of operation. When the armature current of condenser I is leading, the current conducted by the electronic discharge device I0 is lar e, but when the current is lagging, the phase displacement b tween the anode-cathode circuits and the grid leading region of operation it is desirable, and in (I many cases necessary, to permit short-time or transient overloads in this region. To permit such transient overloads in the leading region, the damping circuit 19 has a definite time lag and permits substantial transient overload swings. s

Referring now more particularly to the operation of circuit 41, the electronic discharge device I! varies the voltage of output circuit 82 in a manner to ampliiy the voltage variations of the output circuit of rectifier 4| and filter circuit 42. The entire voltage change, which may be an increment or a decrement of the output voltage of rectifier H, is impressed on the control grid 24 by virtue of the fact that the voltage appearing across the terminals of the glow discharge valve 50 remains constant. In addition, a predetermined component of the instantaneous voltage appearing across the output circuit of rectifier ll is impressed upon the control grid 82. In this manner the electronic discharge device 48 efiects a relatively high amplification of the voltage of circuit ll and hence amplifies changes in the voltage of the alternating current circuit 4, or of the armature voltage of condenser I. Circuit 41 may be arranged so that the point 83 is positive in potential relative to that of point 48' when the power factor of the armature current of condenser l is lagging. Furthermore, the circuit may be arranged so that the potential of point 63 is negative with respect to that of point l8 when the power factor of the armature current of condenser i is leading.

While we have shown and described our invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from our invention, and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, means for controlling the energization of said field winding and comprising a source of alternating current and electric valve means having a control member for controlling the conductivity thereof, voltage controlling means for energizing said control member to control the current conducted by said electric valve means and comprising an electronic discharge device for impressing on said control member a voltage which varies in accordance with the voltage of said armature winding, and means for controlling said voltage controlling means to distinguish between lagging and leading current transmitted by said armature winding and comprising an electric valve having an anode-cathode circuit and a grid circuit, one of which is energized in response to the armature voltage of said machine and the other of which is energized in accordance with the armature current of said machine.

2. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, means for controlling the energization of said field winding comprising a source of alternating current and electric valve means having a control member for controlling the conductivity thereof, voltage controlling means i'or energizing said control memher to controlythe current conducted by said electric valve means in accordance with the voltage or said armature winding and comprising means for impressing on said control member an alternating component oi voltage and an electronic discharge device for superimposing on said alternating component a unidirectional component of voltage which varies in accordance with the voltage 01 said armature winding, and means for controlling said voltage controlling means to distinguish between lagging and leading current transmitted by said armature winding and comprising an electric valve having an anode-cathode circuit and a grid circuit, one of which is energized in response to the armature voltage of said machine and the other of which is energized in accordance with the armature current of said machine.

3. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, mean for controlling the energization of said field winding comprising a source of alternating current and electric valve means having a control member for controlling the conductivity thereof, voltage controlling means for energizing said control mem- .ber comprising an impedance element and an electronic discharge device for transmitting variable amounts of current through said impedance device in accordance with the voltage of said armature winding to impress a variable control voltage on said control member, and means for controlling the voltage across said impedance, element to distinguish between leading and lagging current transmitted by said armature winding and comprising an electric valve having an anode-cathode circuit and a grid circuit, one of which is energized in response to the armature voltage of said machine and the other of which is energized in accordance with the armature current of said machine.

4. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, means for controlling the energization of said field winding comprising a source of alternating current and electric valve means having a control member for controlling the conductivity thereof, voltage controlling means for energizing said control member comprising an impedance element and an electronic discharge device for transmitting variable amounts oi current through said impedance device in accordance with the voltage of said armature winding to impress a variable control voltage on said control member, and means connected across said impedance element for limiting the voltage appearing thereacross and for distinguishing between lagging and leading current transmitted by said armature winding.

5. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, means for controlling the energization of said field winding comprising a source of alternating current and electric valve means having a control member for controlling the conductivity thereof, voltage controlling means for energizing said control member comprising an impedance element and an electronic discharge device for transmitting variable amounts of current through said impedance element in accordance with the voltage of said armature winding to impress a variable control voltage on said control member, and

means associated with said voltage controlling I means andcounprising a second electronic discharge device having'an anode-cathode circuit energized in accordance with the current of said armature winding and having a control circuit energized in accorrhnce with the voltage of said armature winding for distinguishing between lagging and leading Ian-rent transmitted by said armature winding.

6. In, combination, an alternating current dynamo-electric madiine having an armature winding and a field winding, means for controlling the energiaahon at said field winding and comprising a source at alternating voltage and electric valve means having a control member, voltage controlling means for energizing said control member to control the current conducted by said electric valve means in accordance with the voltage of said armature winding, means for controlling said voltage controlling means to distinguish between lagging and leading current transmitted by said armature winding and comprising an electric valve having an anodeca'thode circuit and a grid circuit, one of which is energized in respome to the armature voltage of said machine and the other of which is energized in accordance with the armature current of said machine, and time delay means connected between said last mentioned means and said voltage controlling means.

7. In combination, a synchronous condenser having an armature winding and a field winding, means for controlling the energization of said field winding comprising a source of alternating voltage and electric valve means having a control member, voltage cmtrolling means for energizing said control munher to control the current conducted by said electric valve means in accordance with the voltage of said armature winding, means for cmtrolling said voltage controlling means to distinguish between lagging and leading currmt tramnitted by said armature winding andcanprising an electric valve having an anode-cathode circuit and a grid circuit, one oi which is asergiaed in response to the armature voltage of said machine and the other oi which is energized in response to the armature current of said machine, and a circuit connected between said last mentioned means and said voltage controlling menu to permit only instantaneous increases in the armature current above a predetermined nine in the leading current region.

.8. In combinatim, a synchronous condenser having an armaturewinding and a field winding, meanstor controlling file energization of said field winding and comprising a source 01' alternating current and electric valve means having a control member. voltage controlling means for impressing on said control member a voltage which varies in accordance with the voltage of said armature winding, and electric valve means responsive to the pawnfactor of the armature current for limiting the value oi said voltage to limit the currenttramnitted by said field winding.

9. In combinaimn, an alternating current dynamo-electric machine having an armature winding and field winding, means for controlling the mergimtion of said field winding and comprising a source of alternating current and electric valve means having a control member, a voltage controlling circuit comprising a rectifier for producing a unidirectional voltage which varies in magnitude in accordance with the voltage of said armature winding and a seriallyconnected impedance element and an electronic discharge device connected to be energized irom said rectifier, and an electric valve circuit connected across said impedance element for controlling the voltage' thereof in accordance with the power factor 01' the current transmitted by said armature winding.

10. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, means for controlling the energization of said field winding and comprising a source of alternating current and electric valve means having a control member, a voltage controlling circuit comprising a rectifier for producing a unidirectional voltage which varies in magnitude in accordance with the voltage of said armature winding and a seriallyconnected impedance element and an electronic discharge device connected to be energized from said rectifier, and means connected across said impedance element for controlling the voltage thereacross and comprising an electronic discharge device having anode-cathode and grid circuits, one of said last mentioned circuits being energized in accordance with the voltage of said armature winding and the other of said circuits being energized in accordance with the current of said armature winding.

ll. In combination, an alternating current dynamo-electric machine having an armature winding and a field winding, means for controlling the energization of said field winding and comprising a source 01' alternating current and electric valve means having a control member, a voltage controlling circuit for energizing said control member and comprising a rectifier for producing a unidirectional voltage which varies in magnitude in accordance with the voltage of said armature winding and a serially-connected impedance element and an electronic discharge device connected to be energized from said rectifier, a second impedance element, means for varying the voltage across said second impedance element in accordance with the power factor of the armature current and comprising an electronic discharge device having anode-cathode and grid circuits, one oi. said last mentioned circuits being energized in accordance with the voltage oi said armature winding and the other oi said circuits being energized in accordance with the current of said armature winding, and a unidirectional conducting device connected between said first mentioned and said second mentioned impedance elements.

12. In combination, an alternating current circuit, means for controlling the voltage of said circuit and comprising electric valve means having-a control member, a circuit for impressing a variable voltage on said control member and comprising a rectifier for producing a unidirectional voltage which varies in accordance with said first mentioned voltage and a serially-connected impedance element and an electronic discharge device energized from said rectifier, and means responsive to the power factor of said alternating current circuit for controlling the voltage across said impedance element.

l3. In combination, an alternating current circuit, means for controlling the voltage of said circuit and comprising electric valve means having a control member, a circuit for impressing a variable voltage on said control member and comprising a rectifier ior producing a unidirectional voltage which varies in accordance with said first mentioned voltage and a serially-connected impedance element and an electronic discharge device energized from said rectifier, and means connected across said impedance element for controlling the voltage thereof and comprising an electronic discharge device having anodecathode and grid circuits, one of said last mentioned circuits being energized in accordance with the voltage of said alternating current circuit and the other of said circuits being energized in accordance with the current of said alternating current circuit.

14. In combination, an alternating current circuit, means for controlling the voltage of said circuit and comprising electric valve means having a control member, a circuit for impressing a variable voltage on said control member and comprising a rectifier for producing a unidirectional voltage which varies in accordance with said first mentioned voltage and a serially-comnected impedance element and an electronic discharge device energized from said rectifier, means connected across said impedance element for controlling the voltage thereof and comprising a circuit including an electronic discharge device having anode-cathode and grid circuits, one of said last mentioned circuits being energized in accordance with the voltage of said alternating current circuit and the other of said circuits being energized in accordance with the current of said alternating current circuit, a second impedance element energized by said last mentioned electronic discharge means, and a unidirectional conducting device connected between said first mentioned and said second mentioned impedance elements.

15. In combination, an alternating current circuit, means for controlling the voltage of said circuit and comprising electric valve means having a control member, a circuit for impressing a variable voltage on said control member and comprising a rectifier for producing a unidirectional voltage which varies in accordance with said first mentioned voltage and a serially-connected impedance element and an electronic discharge device energized from said rectifier, means connected across said impedance element for limiting the voltage thereof in accordance with the current and power factor of said alternating current circuit and comprising a circuit including an electronic discharge means having anode-cathode and grid circuits, one of said last mentioned circuits being energized in accordance with the voltage of said alternating current circuit and the other of said circuits being energized in accordance with the current of said alternating current circuit, a second impedance element energized by said electronic discharge means, and an electric valve connected between said first mentioned and said second mentioned impedance elements to conduct current therebetween when the voltage of said second mentioned impedance element attains a predetermined value.

EIMO E. MOYER. ORRIN W. IIV'INGB'I'ON. 

